Law needed Room for Tashigi and his biggest room to date for Vergo. If Law cut Big Mom's Misery without Room, it means Misery is that weak, not that Law is stronger than Zoro.
I think the spoiler provider is wrong about Law cutting Misery. I believe Law used his DF but not awakening. It's only Awakening where he coat his sword.
The spoiler stated Law already had activated a new room.
"Law uses a new technique called “R Room: Silent” which is inspired by Corazón's Nagi Nagi no Mi power. With it, Law creates a sphere around Big Mom that blocks the sounds she makes. This prevents Big Mom voice reaches their nakamas or Kaidou's subordinates."
It wouldn't be surprised if that that room has the powers his normal room just additional powers.